Shrink Slayer Giantess no Yaiba (FULL COMIC) (Gumroad)

When Zenitsu returns after a "special training" he had with Shinobu, Tanjiro will take an interest in it and want to experience the same as his friend, but he did not suspect that the "Insect Hashira" would shrink him to the size of an insect. Now Tanjiro must spend 6 days in the service of 6 beautiful women, and not die trying.

A special thanks to WiredRM for writing a part of the story for this comic.